The puzzles book would be a fun book for your students. I don't remember
anything that would be inappropriate and it is written in such as way as to
be user friendly. Some of the puzzles really stimulate thinking and great
debates. I like this book because it is such a hands-on way to teach ideas
about aesthetics.

I just completed a search on www.abe.com. They have five copies that start
at $20. These must be hardcover. My book is softcover and I paid $3.50 for
it at www.halfpricebooks.com.

The Stewart book is also user friendly, but it's written with the teacher in
mind. It would be a good resource for you to teach from, but probably not
something you'd have the kids read page for page.

If I am not mistaken, there will be an occasional column in SchoolArts this
year that deals with aesthetic issues. If you don't already have a
subscription to SchoolArts, you should consider that, too.
http://www.davis-art.com/schoolarts/subscribe.asp